openGL-绘制四边形网格并手动绘制它们

Question

我正在使用 OpenGL 和 C++ 开发一个简单的图像处理应用程序。但是，有一件事我不知道该怎么做，那就是:

我需要让我的用户绘制直方图。我想这样做的方法是为图像的每个像素强度创建一个四边形网格。示例:如果图像是 8 位，我的网格中需要 256x256 个四边形。绘制网格后，我希望用户以量化的方式(每个四边形)手动绘制四边形，以便他可以“绘制”直方图。问题是我不知道如何做这些事情......谁能指导我如何绘制网格，以及如何制作绘画。

如果您对“绘制直方图”感到困惑，只需将其视为常规图形即可。

Answer 1

您不必绘制四边形网格。一个四边形就足够了，然后使用着色器从存储在一维纹理中的直方图中采样。这是我得到的:

顶点着色器:

#version 450 core
layout(std140, binding = 0) uniform view_block {
    vec2 scale, offset;
} VIEW;

layout(std140, binding = 1) uniform draw_block {
    vec4 position;
    float max_value;
} DRAW;

out gl_PerVertex {
    vec4 gl_Position;
};

void main()
{
    ivec2 id = ivec2(gl_VertexID&1, gl_VertexID>>1);
    vec2 position = vec2(DRAW.position[id.x<<1], DRAW.position[(id.y<<1) + 1]);
    gl_Position = vec4(fma(position, VIEW.scale, VIEW.offset), 0, 1);
}

片段着色器:

#version 450 core
layout(std140, binding = 1) uniform draw_block {
    vec4 position;
    float max_value;
} DRAW;
layout(binding = 0) uniform sampler1D hist;
layout(location = 0) out vec4 OUT;

void main()
{
    const vec2 extent = DRAW.position.zw - DRAW.position.xy;
    vec2 texcoord = (gl_FragCoord.xy - DRAW.position.xy)/(DRAW.position.zw - DRAW.position.xy);
    OUT.rgb = vec3(lessThan(texcoord.yyy*DRAW.max_value, texture(hist, texcoord.x).rgb));
    OUT.a = 1;
}

直方图纹理创建:

image hist(256, 1, 3, type_float);
// ... calculate the histogram ...

tex.reset(glCreateTextureSN(GL_TEXTURE_1D));
glTextureStorage1D(tex.get(), 1, GL_RGB32F, hist.w);
glTextureSubImage1D(tex.get(), 0, 0, hist.w, GL_RGB, GL_FLOAT, hist.c[0]);
glTextureParameteri(tex.get(), GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);

渲染例程:

const vec2i vs = { glutGet(GLUT_WINDOW_WIDTH), glutGet(GLUT_WINDOW_HEIGHT) };
glViewport(0, 0, vs[0], vs[1]);
glClear(GL_COLOR_BUFFER_BIT);

struct view_block {
    vec2f scale, offset;
} VIEW = {
    vec2f(2)/vec2f(vs), -vec2f(1)
};
GLbuffer view_buf(glCreateBufferStorageSN(sizeof(VIEW), &VIEW, 0));
glBindBufferBase(GL_UNIFORM_BUFFER, 0, view_buf.get());

struct draw_block {
    box2f position;
    float max_value;
} DRAW = {
    box2f(0, 0, vs[0], vs[1]),
    max_value
};
GLbuffer draw_buf(glCreateBufferStorageSN(sizeof(DRAW), &DRAW, 0));
glBindBufferBase(GL_UNIFORM_BUFFER, 1, draw_buf.get());

bind_textures(tex.get());
glBindProgramPipeline(pp.get());
glBindVertexArray(0);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

glutSwapBuffers();